1. Field of the Invention
The present invention relates to a film formation method and apparatus for a semiconductor process, which are used for forming a thin film on a target substrate, such as a semiconductor wafer. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target substrate, such as a semiconductor wafer, is subjected to various processes, such as film formation, oxidation, diffusion, reformation, annealing and etching, in general. For example, where a wiring structure is formed, a target substrate is provided with a film of a metal or metal compound thereon, such as W (tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride), TiSi (titanium silicide), Cu (copper), Ta2O5 (tantalum oxide).
In recent years, semiconductor devices have become smaller and more highly integrated, thereby making the design rule on the size of each semiconductor device stricter, i.e., miniaturized. Under the circumstances, capacitors formed of semiconductor devices are therefore required to be further smaller. In this respect, for example, it has been proposed to use a three dimensional device structure, because a larger capacitance can be obtained with the same occupied surface area. Further, in order to increase capacitance, a thin film of a dielectric oxide (a material wit a high dielectric constant), a representative of which is BST (barium strontium titanium oxide), is used as a capacitor insulating film.
It has been studied to use an Ru film (ruthenium film) or RuO2 film (ruthenium oxide film) as a capacitor electrode, so as to reduce the resistance, along with such a capacitor insulating film with a high dielectric constant. Jpn. Pat. Appln. KOKAI Publication Nos. 11-354751, 2001-345285, and 2003-68676 disclose techniques concerning capacitor electrodes of this kind.
FIGS. 7A and 7B are sectional views showing sequential steps of a conventional method for forming an Ru film. Since raw material gases of an Ru film have low surface adsorptivity, it is difficult to directly deposit an Ru film on an underlying layer by CVD (Chemical Vapor Deposition). Accordingly, as shown in FIG. 7A, a seed film 2 of a very thin Ru film is first formed on the underlying layer of a semiconductor wafer W by a sputtering process performed in a sputtering apparatus, which utilizes plasma.
Then, the semiconductor wafer W with the seed film 2 formed thereon is unloaded from the sputtering apparatus and loaded into a CVD apparatus. Then, as shown in FIG. 7B, a CVD process is performed at a high film-formation rate to form a main film 4 of an Ru film over the entire surface of the wafer W including the inner wall of a recess 6. In the CVD process, since the seed film 2 is present below, the Ru film is easily deposited, using the seed film 2 as nuclei. As a consequence, the film is formed on the inner wall of a recess 6 with high step coverage (degree of covering a step portion). This CVD process employs a raw material gases, such as biscyclopentadienyl ruthenium (which may be referred to as Ru(C5H5)2 or Ru(Cp)2), and oxygen gas.